1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) panel, and more particularly, to an LCD panel that is capable of minimizing the movement of a spacer of LCD panel, and a method of fabricating the LCD panel.
2. Discussion of the Related Art
In general, an LCD device utilizes an electric field to control light transmittance of liquid crystal, thereby displaying an image. The LCD device typically includes an LCD panel where liquid crystal cells are arranged in a matrix shape, and a drive circuit for driving the LCD panel. The LCD panel includes pixel electrodes and a reference electrode, i.e., a common electrode, which apply the electric field to the liquid crystal cells. The pixel electrodes are arranged on a lower substrate for the respective liquid crystal cells, whereas the common electrode is integrated into the front surface of an upper substrate. Each of the pixel electrodes is connected to a thin film transistor (TFT) that serves as a switching device. The pixel electrodes together with the common electrode drive the liquid crystal cells in accordance with a data signal supplied through the TFT. The LCD device may be classified either as a twisted nematic (hereinafter, referred to as ‘TN’) mode or an in-plane switch (hereinafter, referred to as ‘IPS’). In accordance with the direction of an electric field that drives the liquid crystal, the TN mode applies a vertical direction electric field, whereas the IPS mode applies a horizontal direction electric field to broaden a viewing angle.
FIG. 1 is a cross sectional view schematically illustrating an LCD panel of the IPS mode according to the related art. As shown in FIG. 1, the LCD panel has a wide viewing angle because a common electrode 28 is arranged on a lower substrate 1 so that liquid crystal 34 can rotate on the basis of a horizontal direction by a horizontal electric field. The common electrode 28 has a stripe shape and is arranged alternately with a pixel electrode 22 in a display area. Moreover, the common electrode 28 is formed of the same metal at the same time as a gate electrode 6 on the lower substrate 1.
A lower plate DP, including the common electrode 28 and the pixel electrode 22, is formed to face an upper plate UP, including an upper substrate 31, a black matrix 2 and a color filter 30. A ball spacer 36 is arranged between the lower plate DP and the upper plate UP to provide a space into which the liquid crystal 34 is injected therebetween. The ball spacer 36 is formed by being sprayed on at least any one of the substrates 1, 31 of the upper plate UP and the lower plate DP, respectively. The ball spacer 36 should be uniformly scattered for uniformly keeping a cell gap of the liquid crystal cell.
Also, as shown in FIG. 1, references 8 and 10 denote source and drain electrodes, reference numerals 14 and 16 denote active layer and contact layer, reference numeral 12 denotes a gate insulating film, 18 denotes a passivation film, and reference numerals 24a and 24b denote upper alignment and lower alignment.
However, it is difficult to uniformly scatter the ball spacer 36 due to a limitation in the uniformity of the scattering method. If the ball spacer 36 is scattered non-uniformly, the cell gap becomes non-uniform, thereby generating a spot on a screen. Moreover, if a pressure is applied to a display area of the LCD panel including the ball spacer 36, the ball spacer 36 moves between the upper plate UP and the lower plate DP, thereby causing a ripple phenomenon, which causes an image displayed in the display area to become dark in a wave shape.
In order to resolve the above problems of the ball spacer 36, it is suggested to fix and pattern a column spacer at a specific location. However, since the column spacer is formed by a photolithography process, in which more than 95% of a spacer material is removed, the usage rate of the material is very low and also the fabrication processes are complicated. In order to improve the usage rate of the material and simplify the fabrication processes, there has been developed a method for forming a ball spacer utilizing an ink-jet spraying device. This method can control the location of forming the ball spacer, which is different from the ball spacer scattering method that has the limitation in the uniformity thereof.
FIG. 2 is a view schematically showing an example of a spacer arrangement of an LCD panel according to the related art. As shown in FIG. 2, the ball spacers 36 are formed by the ink-jet method. In order to prevent the ball spacers 36 from moving between the upper plate UP and the lower plate DP, the ball spacers 36 are disposed at a fixed point such that the ball spacers 36 are each formed in a groove at a location where the ball spacers 36 are to be formed between the upper and lower plates.
However, the ball spacers 36 may be moved by a pressure, shock, impact, etc., which are applied in a process after the ball spacer 36 has been formed. FIG. 3 is a view schematically showing an exemplary phenomenon in that the ball spacers 36 of FIG. 2 are moved in a process after they have been arranged. As shown in FIG. 3, even though the ball spacers 36 have each been arranged by the ink-jet method at the fixed point with the groove formed at the desired location as shown in FIG. 2, the ball spacers 36 are moved as shown in FIG. 3 due to the pressure, shock or impact. Accordingly, in the related art, since the ball spacers 36 are moved in the display area of the color filter 30, the uniformity of the cell gap and the contrast ratio are deteriorated.
FIG. 4 is a plan view showing part of a thin film transistor (TFT) array substrate of the IPS mode as another example according to the related art. As shown in FIG. 4, the TFT array substrate includes a gate line 42 and a data line 44 that are arranged crossing each other on a lower substrate, a TFT 60 that is formed at each crossing part of the gate and date lines 42 and 44, a pixel electrode 52 and a common electrode 54 that are arranged to form a horizontal electric field in a pixel area 45 provided in the crossing structure, and a common line 56 that is connected to the common electrode 54.
The pixel electrode 52 consists of a first pixel electrode 52a in parallel to the gate line 42 and a second pixel electrode 52b in parallel to the data line 44. The common line 56 together with the first pixel electrode 52a forms a storage capacitor 70/80 with a gate insulating film (not shown) therebetween. The TFT 60 serves to make a pixel signal of the data line 44 charged and maintained in the pixel electrode 52 in response to a gate signal of the gate line 42. To this end, the TFT 60 is provided with a gate electrode connected to the gate line 42, a source electrode 48 connected to the data line 44, and a drain electrode 50 connected to the pixel electrode 52. The source electrode 48 consists of a first source part 48b projected from the data line 44 and a second source part 48a formed in a ‘U’ shape by being projected in two directions from the first source part 48b. The drain electrode 50 is formed to face the second source part 48a of the source electrode 48 with a channel of the ‘U’ shape therebetween. Moreover, the drain electrode 50 is connected to the first electrode part 52a of the pixel electrode 52 through a contact hole 53. However, in the related art as shown by FIG. 4, a space for forming a ball spacer is not secured between the gate line 42 and the storage capacitor 80 adjacent to the thin film transistor 60.